The invention relates to a bath for anodizing aluminized parts, which is a formulated sulfuric acid aqueous solution and contains additives, as well as to a method for preparing anodizing layers, which is carried out using such a bath.
Aluminum materials and aluminum-coated parts are not yet resistant enough to oxidation and wear for many applications, although a resistant oxide coating which is stable in the pH range of 5 to 9 is produced in air. This oxide layer, however, is still too thin for many technical applications. Therefore, the layer can be reinforced in anodizing electrolytes.
Use of known acid anodizing baths to anodize partially aluminized articles such as ferrous materials not coated in contact areas, or those profiled parts having uncoated places which may exist due to the limited throwing power in non-aqueous aluminum baths and in the case of vapor deposition processes, requires covering the exposed areas with a so-called masking film prior to anodizing. Otherwise, the base material is dissolved anodically. After the anodizing, such varnishes must be removed either by stripping them off or dissolving them with a suitable solvent. In the case of cavities or holes in which there is no aluminum, the situation can be corrected by sealing them with plugs or the like. This procedure, while technically possible in principle, is technically expensive and uneconomical.
It is therefore an object of the invention to develop a bath for anodizing aluminized parts, in which the disadvantages described above do not occur and by means of which it is, in particular, possible to generate homogeneously coherent sufficiently thick oxide layers when the base material surface is not covered with aluminum on all sides.